The present invention relates to an apparatus and a method for spine fixation, and more particularly to a spine fixation assembly utilizing plates.
The human spine 29 comprises individual vertebrae 30 that interlock with each other to form a spinal column, shown in FIG. 1A. Referring to FIGS. 1B and 1C, each vertebra 30 has a cylindrical bony body (vertebral body) 32, three winglike projections (two transverse processes 33, 35 and one spinous process 34), and a bony arch (neural arch) 36. The bodies of the vertebrae 32 are stacked one on top of the other and form the strong but flexible spinal column. The neural arches 36 are positioned so that the space they enclose forms a tube, i.e., the spinal canal 37. The spinal canal 37 houses and protects the spinal cord and other neural elements. A fluid filled protective membrane, the dura 38, covers the contents of the spinal canal. The spinal column is flexible enough to allow the body to twist and bend, but sturdy enough to support and protect the spinal cord and the other neural elements.
The vertebrae 30 are separated and cushioned by thin pads of tough, resilient fiber known as inter-vertebral discs 40. Inter-vertebral discs 40 provide flexibility to the spine and act as shock absorbers during activity. There is a small opening (foramen) 42 between each vertebra 30, through which nerves 44 pass and go to different body parts. When the vertebrae are properly aligned the nerves 44 pass through without a problem. However, when the vertebrae are misaligned or a constriction 45 is formed in the spinal canal, the nerves get compressed 44a and may cause back pain, leg pain or other neurological disorders. Disorders of the spine that may cause misalignment of the vertebrae or constriction of the spinal canal include spinal injuries, infections, tumor formation, herniation of the inter-vertebral discs (i.e., slippage or protrusion), arthritic disorders, and scoliosis. In these pathologic circumstances, surgery may be tried to either decompress the neural elements and/or fuse adjacent vertebral segments. Decompression may involve laminectomy, discectomy, or corpectomy. Laminectomy involves the removal of part of the lamina 47, i.e., the bony roof of the spinal canal. Discectomy involves removal of the inter-vertebral discs 40. Corpectomy involves removal of the vertebral body 32 as well as the adjacent disc spaces 40. Laminectomy and corpectomy result in central exposure of the dura 38 and its contents. An exposed dura 38 puts the neural elements and spinal cord at risk from direct mechanical injury or scarring from overlying soft tissues. After laminectomy and corpectomy the surgeon needs to stabilize the spine with a fusion. Fusion involves the fixation of two or more vertebrae. Fusion works well because it stops pain due to movement of the intervertebral discs 40 or facets 46, immobilizes the spine, and prevents instability and or deformity of the spine after laminectomy or corpectomy. Finally a bone graft (202 shown in FIG. 6), i.e., a solid piece of bone (1-2 inches) or bone chips, is inserted between laterally adjacent transverse processes and/or pars.
Several spinal fixation systems exist for stabilizing the spine so that bony fusion is achieved. The majority of these fixation systems use either plates or rods that attach to screws inserted into the vertebral body or the pedicles 48, shown in FIG. 1C. Plate fixation systems are more commonly used in the anterior part of the spine, i.e., vertebral bodies, while rods are the accepted standard for posterior fixation. In some cases plate fixation systems are also used to fuse two adjacent vertebral segments. This construction usually consists of two longitudinal plates that are each placed laterally to connect two adjacent pedicles of the segments to be fused. This system can be extended along the sides of the spine by connecting two adjacent pedicles at a time similar to the concept of a bicycle chain. Current plate fixation systems are basically designed to function in place of rods with the advantage of allowing intersegmental fixation without the need to contour a long rod across multiple segments.
Single or multilevel segmental posterior fusions are most commonly achieved by contouring a solid xc2xcinch cylindrical rod and attaching it to adjacent pedicle screws on each side of the spine using various connecting assemblies. This longitudinal construction can be made more rigid by connecting the rods to each other to form an xe2x80x9cHxe2x80x9d configuration.
The rod system requires contouring of each rod across several vertebras in many cases. The contouring of each rod depends on the configuration of the pedicle screws and varies from side to side in the same patient and among patients. This may add considerable time to an operation. Recent generations of pedicle screws and rod connectors seek to diminish this drawback by allowing variable axes of movements in the pedicle screw recess for the rod or in the rod connectors. However, in most cases this adds another level of complexity to the operation and often further increases the operative time. This increase in operative time and the complexity of the connectors put substantial stress on the surgeon and the supporting staff. Even in the hands of the best spine surgeon, the rod is often not perfectly contoured to align with the pedicle screws. Hence the surgeon has to use substantial force at multiple points along a rod to hold the rod to the screws or connectors while counteracting the adjacent soft tissues. This maneuver risks soft tissue damage and also puts the dura and the neural contents at risk for dural tears or spinal cord or nerve damage if a holding instrument slips. The added bulk of the rods and connectors along the lateral aspect of the spine limits access to the pars and transverse processes for decortication and placement of bone graft. Some of the current plating systems have the same limited access to the pars and/or transverse processes. In order to avoid this limitation many surgeons decorticate before placing the rods, thereby increasing the amount of blood loss and making it more difficult to maintain a clear operative field. Placing rods or plates lateral to the spine leaves the center of the spinal canal that contains the dura, spinal cords and nerves completely exposed. In situations where problems develop at the junction above or below the fused segments necessitating additional fusion, the rod fixation system is difficult to extend to higher or lower levels that need to be fused. Although there are connectors and techniques to lengthen the fixation, they tend to be difficult to use and time consuming.
In general, in one aspect, the invention features a spine fixation assembly connecting a first and second vertebra. The spine fixation assembly includes a first elongated plate having a first and second end and a second elongated plate having a first and second end. The first and second ends of the first plate are adapted to be attached to a first location of the first vertebra and to a second location of the second vertebra, respectively. The first and second ends of the second plate are adapted to be attached to a second location of the first vertebra and to a first location of the second vertebra, respectively. The first and second elongated plates form an X-shaped structure and may be cross-coupled. The locations where the ends of the plates may be attached include a pedicle, transverse processes, pars, lamina, vertebral body, sacrum, lateral mass, and occiput.
Implementations of this aspect of the invention may include one or more of the following features. The first and second elongated plates are cross-coupled and attached to each other via a screw. The spine fixation assembly may further include a third elongated plate having a first and second end. The first and second ends of the third plate are adapted to be attached to the first and second locations of the first vertebra, respectively. The spine fixation assembly may further include a fourth elongated plate having a first and second end. The first and second ends of the fourth plate are adapted to be attached to the first and second locations of the second vertebra, respectively. The first and second vertebra may be adjacent to each other. The ends of the elongated plates may be attached to the locations of the vertebrae via screws or hooks. The screws may include a body portion, a first head portion connected to the body portion, a second head portion connected to the first head portion, and a head connected to the second head portion. The body portion has a threaded outer surface for screwing into the locations of the vertebrae. The first head portion has a serrated or a smooth outer surface for receiving an end of the elongated plates, the end having an aperture for sliding over the first head portion, and the aperture has a serrated or smooth inner surface interlocking with the serrated or smooth outer surface of the first head portion, respectively. The second head portion has a threaded outer surface for receiving a washer with matching inner threads. The head has a slot for receiving a screwdriver. The screws may be made of stainless steel, titanium, gold, silver, alloys thereof, or absorbable material. The elongated plates may be made of metal, plastic, ceramic, bone, absorbable material, composites, or combinations thereof. The elongated plates may have a length in the range of 20 millimeters to 200 millimeters. The elongated plates may be flat close to the center of the plate and arch downward towards the first and second ends. The length of the elongated plates may be adjustable. The elongated plates may include a first and a second segment and the first and second segments are connected to each other. The first and second segments are connected to each other via a sliding mechanism, and this sliding mechanism provides an adjustable length of the elongated plates. The elongated plates may include a first and a second component and the first and second component can rotate relative to each other and around a central axis passing through the center of the X-shaped structure. The ends of the elongated plates may be circular and have an aperture for sliding over a screw positioned in the locations of the vertebrae. The aperture may have a serrated inner surface interlocking with a serrated outer surface of the screw. The circular ends may have grooves on their top and bottom surfaces. The grooves may be spaced ten degrees apart from each other. A washer having a grooved bottom surface may be adapted to be placed on the top surface of the end of the elongated plate. The washer grooves interlock with the grooves on the top surface of the end of the elongated plate. The elongated plates may have a circular center and the center may have an aperture for receiving a screw. The aperture of the circular center may have a threaded inner surface interlocking with a threaded outer surface of the screw. The top surface of the circular center may have grooves which are spaced ten degrees apart from each other
In general, in another aspect, the invention features a spine fixation apparatus connecting a plurality of pairs of a first and a second vertebra. The spine fixation apparatus according to this aspect includes a plurality of first elongated plates each first plate having a first and second ends, a plurality of second elongated plates having a first and second ends, and the pluralities of the first and second elongated plates form a plurality of X-shaped structures that are connected to each other. The first and second ends of the first plates are adapted to be attached to a plurality of first location of the plurality of first vertebra and to a plurality of second location of the plurality of second vertebra, respectively. The first and second ends of the second plates are adapted to be attached to a plurality of second location of the plurality of first vertebra and to a plurality of first location of the plurality of second vertebra, respectively. The first and second elongated plates form a plurality of X-shapes and may be cross-coupled. The spine fixation apparatus may further include a third elongated plate having first and second ends, and the first and second ends of the third plate may be adapted to be attached to the first and second locations of the first vertebra, respectively. The spine fixation apparatus may further include a fourth elongated plate having a first and second end, and the first and second ends of the fourth plate are adapted to be attached to the first and second locations of the second vertebra, respectively.
In general, in another aspect, the invention features a spine fixation assembly connecting a first and a second vertebra including a central structure, first, second, third and fourth elongated plates. The first elongated plate has a first end adapted to be attached to the central structure and a second end adapted to be attached to a first location of the first vertebra. The second elongated plate has a first end adapted to be attached to the central structure and a second end adapted to be attached to a second location of the first vertebra. The third elongated plate has a first end adapted to be attached to the central structure and a second end adapted to be attached to a first location of the second vertebra, and the fourth elongated plate has a first end adapted to be attached to the central structure and a second end adapted to be attached to a second location of the second vertebra.
Implementations of this aspect of the invention may include one or more of the following features. The central structure may have a circular or rectangular shape. The elongated plates may have adjustable length and the length may be in the range of 10 millimeters to 200 millimeters. The second ends of the elongated plates may be attached to the locations of the vertebrae via screws or hooks. The first ends of the elongated plates may be attached to the central structure allowing rotational movement around an axis passing through the central structure and are secured via screws or a ring.
In general, in another aspect, the invention features a spine fixation method connecting a first and second vertebra including the following steps. First, providing a first elongated plate having a first and second ends and attaching the first and second ends of the first plate to a first location of the first vertebra and to a second location of the second vertebra, respectively. Next, providing a second elongated plate having a first and second ends and attaching the first and second ends of the second plate to a second location of the first vertebra and to a first location of the second vertebra, respectively. The first and second plates form an X-shaped structure. The method may further include cross-coupling the first and second elongated plates. The method may further include providing a third elongated plate having first and second ends and attaching the first and second ends of the third plate to the first and second locations of the first vertebra, respectively. The method may further include providing a fourth elongated plate having first and second ends and attaching the first and second ends of the fourth plate to the first and second locations of the second vertebra, respectively.
In general, in another aspect, the invention features a spine fixation method connecting a first and second vertebra including the following steps. First attaching first and second screws to first and second locations of the first and second vertebra, respectively. Then, attaching third and fourth screws to second and first locations of the first and second vertebra, respectively. Next, providing a first elongated plate having a first and second ends and attaching the first and second ends of the first elongated plate to the first location of the first vertebra and to a second location of the second vertebra via the first and second screws, respectively. Next, providing a second elongated plate having a first and second ends and attaching the first and second ends of the second elongated plate to the second location of the first vertebra and to the first location of the second vertebra via the third and fourth screws, respectively. The first and second elongated plates form an X-shaped structure. Finally cross-coupling the first and second elongated plates by placing a central screw through the center of he X-shaped structure; and tightening of all said screws. The method may further include adjusting the length of the first and second elongated plates.
In general, in another aspect, the invention features a spine fixation method connecting a first and second vertebra including the following step. First, attaching first and second screws to first and second locations of the first and second vertebra, respectively. Next, attaching third and fourth screws to second and first locations of the first and second vertebra, respectively. Then, providing a first elongated plate having a first and second ends and a center, and attaching the first and second ends of the first elongated plate to the first location of the first vertebra and to a second location of the second vertebra via the first and second screws, respectively. Then providing a second elongated plate having first and second ends, and attaching the first and second ends of the second elongated plate to the second location of the first vertebra and to the center of the first elongated plate via the third screw and a fifth screw, respectively. Then, providing a third elongated plate having first and second ends, and attaching the first and second ends of the third elongated plate to the first location of the second vertebra and to the center of the first elongated plate via the fourth and fifth screws, respectively. Finally, tightening of all the screws. The method may further include adjusting the length of the first, second, and third elongated plates.
In general, in another aspect, the invention features a spine fixation method connecting a first and second vertebra including the following steps. First, attaching first and second screws to first and second locations of the first vertebra, respectively. Next, attaching third and fourth screws to first and second locations of the second vertebra, respectively. Then providing a central structure having fifth, sixth, seventh and eighth screws. Next, providing a first elongated plate having first and second ends, and attaching the first and second ends of the first elongated plate to the first location of the first vertebra and the central structure via the first and fifth screws, respectively. Next, providing a second elongated plate having a first and second ends, and attaching the first and second ends of the second elongated plate to the second location of the first vertebra and to the central structure via the second and a sixth screws, respectively. Next, providing a third elongated plate having a first and second ends, and attaching the first and second ends of the third elongated plate to the first location of the second vertebra and to the central structure via the third and seventh screws, respectively. Next, providing a fourth elongated plate having a first and second ends, and attaching the first and second ends of the fourth elongated plate to the second location of the second vertebra and to the central structure via the fourth and eighth screws, respectively. Finally, tightening of all the screws. The method may further include adjusting the length of the first, second, third, and fourth elongated plates.
In general, in yet another aspect, the invention features a spine fixation method connecting a first and second vertebra including the following steps. First attaching first and second screws to first and second locations of the first vertebra, respectively. Next, attaching third and fourth screws to first and second locations of the second vertebra, respectively. Next, providing a pair of first and second elongated plates forming an X-shaped structure and then placing the X-shaped structure over the first and second vertebra. Next, attaching a first and a second end of the first elongated plate to the first location of the first vertebra and the second location of the second vertebra via the first and fourth screws, respectively. Next, attaching a first and a second end of the second elongated plate to the second location of the first vertebra and to the first location of the second vertebra via the second and third screws, respectively. Finally, tightening of all said screws. The method may further include adjusting the length of the first and second elongated plates.
Among the advantages of this invention may be one or more of the following. The spine fixation assembly of this invention provides a rigid and compact structure. It has low side and front profiles and does not interfere with the lateral soft tissues and bones. The basic X-shaped structure increases the available area for bone grafting and provides easy access to the transverse processes 230, 232 and pars 234, 236 for bone graft 202, 204 placement after implanting the spine fixation assembly, shown in FIG. 6. The flexibility in length and orientation of the plates allows the assembly to be adapted to non-symmetric spinal anatomies. The basic X-shape structure is repeated to extend the spine fixation in either caudad or cephalad directions either at the initial surgery or during revision. This allows a surgeon to perform short or long spinal fusions, correct spinal deformities, extend the fusion at revision, or remove the fixation at one or more fused levels to revise a part of the fusion with ease. The modular plates couple to each other and the pedicle screws without the need to apply excessive retraction on the surrounding soft tissues. This reduces the injury risk of the surrounding soft tissue, bones, and neural elements during placement of the plates. Furthermore, the cross-coupled plates cover and protect the midline and spinal canal of the patient from direct injury or possible scarring from overlying soft tissues.